The present invention is directed, to polishing pads used for creating a smooth, ultra-flat surface on such items as glass, semiconductors, dielectric/metal composites, magnetic mass storage media and integrated circuits. More specifically, the present invention relates to the transformation of thermal conductive properties to create more suitable polishing pads.
Chemical-mechanical polishing (CMP) is used increasingly as a planarizing technique in the manufacture of VLSI integrated circuits. Although it has the potential for planarizing a variety of materials in IC processing, CMP is used most widely for planarizing metallizied layers and interlevel dielectrics on semiconductor wafers, and for planarizing substrates for shallow trench isolation.
There are three critical consumable components in the CMP process. The first is the abrasive liquid slurry. The abrasive liquid slurry""s composition must be altered, and special formulations must be produced for each different substrate being polished. For example, some substrates require a high pH to be activated for polishing, while other substrates need a more acidic environment. Still other substrates respond best to silica abrasives, while others require alumina or titanium abrasive particles. The second critical consumable component in the CMP process is the polishing pad. It must be very flat, uniform across its entire surface, and resistant to the chemical nature of the slurry and have the right combination of stiffness and compressibility to minimize effects like dishing and erosion. A third critical consumable component in the CMP process is the carrier film. The carrier film attached the wafer to its rotating holder must have an adequate flatness, be uniform in its thickness, have adhesive properties that will hold it tightly to the carrier but not too tightly to the wafer, and be immune to the chemical environment in which it works.
During conventional CMP of metal stacks, an oxidant is used to convert the top metal to metal oxides. These metal oxides are subsequently abraded in situ with harder metal oxide abrasives. The oxidation of the top metal is invariably an exothermic process, which leads to enhanced process temperatures. Thus, in addition to the heat from the frictional forces inherent in CMP, heat is also generated from the oxidation of the metallic film.
During metal CMP, areas dense in features (i.e., alignment marks) tend to erode at a faster rate than areas with sparse distributions. This uncontrollable erosion of the metals forming the alignment marks is commonly referred to as oxide erosion. Additionally, manufacturers have observed that oxide erosion in dense arrays increase dramatically as batch sizes are increased.
As noted above, heat is a byproduct of the oxidation process. Increased temperatures affect the mechanical properties of the metal oxide film by making films easier to abrade. But the resulting enhanced abrasion rate results in recessed metal plugs that are separated by thin oxide walls that rapidly collapse with polishing, thereby leading to oxide erosion. It has been found that a reduction in temperature reduces the solubility of by-products, which correspondingly reduces the oxide erosion.
Based on observations of variations in polishing rates it was concluded that the polishing rate differential across a wafer was primarily due to temperature variations across the wafer during the polishing operation. These temperature variations may result from: 1) non-uniformities in the heat transfer characteristics of the wafer carrier, 2) accelerated chemical reactions due to non-uniform reactant concentrations, 3) non-uniform heating of the slurry, or 4) non-uniform heating of the wafer itself due to differences in the amount and duration of friction generated between different parts of the wafer being polished. These effects do not necessarily have a pattern, although isotherms may develop in a circular pattern due to the rotation of the wafer. In such instances, the temperature gradients therefore typically have a radial pattern.
Several approaches have been proposed to address these deficiencies in the art. Tight temperature control of the polishing platen has been proposed as a means to control excessive heating. However, this does not address or resolve problems due to temperature variations across the surface of the substrate during polishing. Moreover, the polishing pad is typically a layered polymer materials with layers having different hardness, depending on the CMP process being used, and the material being removed from the wafer. And, because these pads are thermally insulating, they do not efficiently conduct away the unwanted heat from the process, even when the polishing platen is cooled.
An alternative approach is to use a temperature controlled wafer carrier for CMP. The wafer carrier comprises a polishing head having a circular recess with cooling coils embedded in the polishing head situated close to the recess. The coils allow coolant to circulate through the wafer carrier. This reduces temperature gradients by providing local temperature control means in the head of the wafer carrier.
Another approach is to planarize a surface on a semiconductor wafer containing metal with reduced temperature slurries. This provides a method in which the rate of oxidation is reduced to inhibit uncontrolled oxide formation. The reduced slurry temperature also reduces the solubility of the process by-products in the slurry thus passivating dielectric surfaces against erosion.
Yet another approach involves modifying the surface of CMP pads materials to improve the wetability of the pad surface and the adhesion of surface coatings, thereby increasing the application performance of these materials. Plasma treatment of polishing pad materials is one means to functionalize and thereby modify polishing pad surfaces. However, the functionalization of pad surfaces by plasma treatment is subject to post-treatment surface energy hysteresis and the spontaneous return to low surface energy conditions after a short period.
Not withstanding the foregoing attempts at thermal management, the problem of effective thermal management still persists in the art. Accordingly, what is needed in the art are materials and methods for controlled and predictable thermal management and the dissipation of heat generated from the friction and chemical events inherent in the polishing process.
To address the deficiencies of the prior art, the present invention, in one embodiment, provides a heat conductive polishing pad for chemical-mechanical polishing. The pad comprises a polishing body including a thermoconductive polymer having a substrate with filler particles contained therein. The filler particles contain a Group II salt.
In another embodiment, the present invention provides a method for preparing a heat conductive plastic polishing pad for chemical-mechanical polishing. The method comprises providing a substrate, blending filler particles containing a Group II salt into the substrate to thereby produce a thermoconductive polymer. The method further includes forming a polishing body from the thermoconductive polymer suitable for polishing a semiconductor wafer or integrated circuit.
Yet another embodiment provides a polishing apparatus. The apparatus comprises a mechanically driven carrier head, a polishing platen and a polishing pad attached to the polishing platen. The carrier head is positionable against the polishing platen to impart a polishing force against the polishing platen. The polishing pad includes a polishing body comprising a thermoconductive polymer having a substrate with filler particles containing a Group II salt as described above.
The foregoing has outlined preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention.